1. Field of the Invention
The present invention relates generally to the field of ophthalmic devices, more particularly to intraocular lenses (IOLs), and still more particularly to thin profile monofocal refractive IOLs for implanting in narrow ocular regions, especially the anterior chamber of an eye.
2. Background Discussion
The following definitions are considered helpful to the understanding of the present invention:
The term “phakic” applies to an eye in which the natural crystalline lens is still present.
The term “aphakic” applies to an eye from which the natural crystalline lens has been surgically removed, for example, due to the formation of cataracts on the lens.
The anterior chamber of an eye is the narrow region between the back, endothelial surface of the cornea and the front surface of the iris.
The posterior chamber of a phakic eye is the narrow region between the back surface of the iris and the front surface of the natural crystalline lens.
A Fresnel lens (as defined at page 167 of the DICTIONARY OF OPTICS, published by Butterworth Heinemann, 1995) is “A lens surface of narrow concentric rings or prism sections of a specified power that gives the effect of a continuous lens surface with the same power, but without the usual thickness and weight.
Glare (as defined at page 53 of THE GLOSSARY OF OPTICAL TERMINOLOGY, published by Professional Press Books, Fairchild Publications, 1986) is “Any degree of light falling on the retina in excess of that which enables one to see clearly.” And alternatively as “Any excess of light which hinders rather than helps vision. (Too much light in the wrong place.)”
Vision in a phakic eye is caused by light from a viewed object being refracted by the cornea and the natural crystalline lens to form an image on the retina at the back of the eye. Corrective spectacles, contact lens or corneal reshaping may be used to assist such image formation. Optical muscles connected to a normal crystalline lens change the shape of the lens as needed to provide images of objects at different distances from the eye, an optical process known as accommodation.
The prevailing procedure for restoring vision (except for accommodation) in an aphakic eye is the surgical implanting of a refractive artificial lens, called an intraocular lens (TOL), ordinarily in the capsular bag from which the natural lens has been removed.
In addition to continued development of TOLs for restoring vision in aphakic eyes, considerable attention has recently been directed toward developing refractive IOLs (and insertion instruments) for implanting in the anterior chamber of phakic eyes having normal crystalline lenses to correct such vision defects as myopia, hyper-metropia, presbyopia and astigmatism. The implanting of such corrective IOLs can potentially eliminate the wearing of spectacles or contact lenses, and/or eliminate permanent surgical procedures involving the cornea.
Anterior chamber-type IOLs may alternatively be implanted in posterior chambers of phakic eyes for providing corrective power to the natural lens, as may be needed due to subsequent physiological changes of the natural lens as an individual ages.
The anterior chamber is generally dome-shaped and very narrow—typically only about 3 mm at its center. The posterior chamber of a phakic eye be even more narrow, depending upon the size of the crystalline lens and the amount of its accommodation the width of the posterior chamber of a phakic eye—the successful implanting of a corrective IOL in either of these ocular chambers is extremely difficult and risks injuring delicate ocular tissue, especially the cornea's endothelial surface in the case of anterior chamber implanting. Consequently, refractive corrective IOLs, particularly the IOL optics, are desirably made as thin as possible consistent with providing the requisite corrective power and structural stability of the optic.
To this end, several known patents disclose the use of a Fresnel lens on one surface of a refractive IOL optic. For example, U.S. Pat. No. 4,673,406 to Schiegel (issued Jun. 16, 1987) discloses a one-piece foldable refractive IOL with one surface of its central lens body formed as a Fresnel lens to reduce the thickness of the optic to enable the IOL to be implanted in a folded condition into an eye through a small corneal incision. The patent further discloses that individual zones of the multi-zone Fresnel lens are selected such that the focal points of all the zones coincide so as to reduce spherical aberration. As another example, U.S. Pat. No. 4,787,903 to Grendahl (issued Nov. 29, 1988) discloses a refractive IOL or corneal lens having an optic that incorporates a Fresnel lens with multiple, concentric ring-zones. The Grendahl lens is further disclosed as being made of a composite material that allows refractive index modification with electromagnetic energy. (The Grendahl patent asserts a first use of a Fresnel lens for IOLs or corneal lenses, the Grendahl patent application having been filed shortly before the Schiegel patent application was filed).
As still further examples, U.S. Pat. No. 4,846,833 to Cumming (issued Jul. 11, 1989) discloses the forming of a Fresnel lens on the back surface of a posterior chamber IOL so the Fresnel surface will be sealed by the posterior capsule surface upon the implanting of the IOL in an aphakic eye. U.S. Pat. No. 6,096,077 to Callahan et al. (issued Aug. 1, 2000) discloses a thin IOL having the posterior surface formed of a stepped series of annular concentric rings of increasing diameter surrounding a central planar disc region; although, the Callahan et al. patent does not specifically identify the IOL posterior surface as being a Fresnel lens, the associated figures indicate that such is the case.
A characteristic common to the four above-cited patents is that the Fresnel zones comprise a series of staircase-like concentric zones separated from one another by abrupt transition steps. None of the Specifications of the cited patents describe these transition steps, however the accompanying figures depict the transition steps as having flat transition surfaces that are parallel to one another and to the optical axis of the optic, as are all Fresnel lenses. Moreover, none of the above-cited patents disclose any glare effects that may be caused by the flat transition steps between Fresnel zones.
As shown below by the present inventor, IOLs having abrupt Fresnel zone transition steps with flat surfaces induce substantial distracting and potentially hazardous glare in the IOL wearer's eye when light (especially bright light) impinges on the lens optic as, for example, is commonly encountered in night driving or when driving into the sun.
Accordingly, a principal objective of the present invention is to provide a narrow profile (that is, thin) IOL, in particular, a narrow profile monofocal IOL that substantially minimizes such visual glare problems.
In addition to minimizing glare at imaging zone transition steps in thin IOLs it is desirable to minimize glare from IOL optic peripheral edges, while still maintaining thinness of the optic. In this regard it is known that a reduction on optic thickness can be achieved by reducing the optic diameter. However, optic diameter reduction may result in glare due to light passing outside the optic diameter. Such optic edge glare may be direct, indirect or combined direct and indirect glare according to lighting conditions encountered by an individual in whose eye the IOL is implanted. Indirect and direct glare are most likely to be encountered at night under driving conditions in which the IOL wearer encounters bright lights, such as streetlights, traffic lights and/or headlights and taillights on other vehicles and the individual's pupil diameter is large enough to expose regions outside the IOL optic diameter (as is likely under night driving conditions). The effects of such glare include halos around light sources and blurred vision.
A principal objective of the present invention is therefore to provide a narrow profile (thin) IOL having a large optic diameter peripheral edge region shaped to minimize direct and/or indirect glare caused by light impinging on the optic peripheral edge.